Electrochemical synthesis method and device

ABSTRACT

The present invention relates to a method for producing at least one product by electrochemical synthesis on a directly electrically-heated working electrode ( 1 ), in which at least one educt reacts on the heated working electrode ( 1 ) to the at least one product. The invention also relates to the use of a directly electrically-heated working electrode ( 1 ) for the electrochemical synthesis of at least one product. The invention relates in particular to a working electrode ( 1 ), particularly in the form of a three-dimensional, preferably conical spiral, designed for the electrochemical synthesis. Another object of the invention is the synthesis/regeneration of an enzymatic cofactor on a working electrode ( 1 ) according to the invention.

The present invention relates to a method for producing at least oneproduct by electrochemical synthesis on a directly electrically-heatedworking electrode (1), in which at least one educt reacts on the heatedworking electrode (1) to the at least one product. The invention alsorelates to the use of a directly electrically-heated working electrode(1) for the electrochemical synthesis of at least one product. Theinvention relates in particular to a working electrode (1), particularlyin the form of a three-dimensional, preferably conical spiral, designedfor the electrochemical synthesis. Another object of the invention isthe synthesis/regeneration of an enzymatic cofactor on a workingelectrode (1) according to the invention.

In the prior art, heated working electrodes are used for trace analysisin voltammetry, amperometry/coulometry and potentiometry, and they can,for example, be directly heated by means of alternating current orindirectly by means of alternating current or direct current.

In the case of indirect heating, the working electrode can beconstructed from several concentric or parallel layers, which aregalvanically separated from one another, the outermost layer serving asan electrode and an inner layer serving as a heating element. Indirectheating by means of heaters galvanically separated from the electrode isdisadvantageous, because the construction of the sensors is morecomplicated, the temperature changes are generally slower because of thethermal inertia (due to the heat capacity) of the different layers, andthe possibilities for miniaturization are limited.

Various directly-heatable working electrodes, in which the heatingcurrent as well as the electrolysis current, i.e., the current for theelectrochemical measurement signal, flow together through the sameconductor, are known from the prior art.

Direct electrical heating of the working electrode and simultaneousinterference-free electrochemical measurement can be performed accordingto the prior art by a so-called symmetrical arrangement or specialfilter circuits. One variant of the directly-heated working electrodehas a third contact for connection to the electrochemical measuringdevice, situated precisely in the middle between the two contacts whichsupply the heating current. This arrangement prevents interferinginfluences of the heating current on the measuring signals. Adisadvantage is the complex design with three contacts per workingelectrode, the thermal disturbance due to the heat-dissipating thirdcontact and the complicated miniaturization. In a preferred embodimentaccording to the invention, therefore, a symmetrical contacting iseffected by means of a bridge circuit, which allows direct heating(Wachholz et al., 2007, Electroanalysis 19, 535-540, in particular FIG.3; Dissertation Wachsholz 2009). Thereby, the working electrode can bearranged so that the temperature distribution on the surface of theworking electrode is uniform (DE 10 2004 017 750). DE 10 2006 006 347discloses advantageous directly electrically heatable electrodes.

According to the prior art, there are various kinds of directly heatedworking electrodes and arrays. The oldest variant of a single electrodeis based on circuit boards which have corresponding recesses (wideslots) and an electrical insulation with a paraffin-PE mixture. Here,wire electrodes of gold or platinum are typically soldered. The wirediameter is usually 25 micrometers (P. Gründler et al., Chem. Phys.Chem. 10 (2009) 559).

In addition, layered electrodes and arrays have been proposed. Printedcircuit boards, glass, and plastic were specified as substrates.

In all layered constructions, there is the disadvantage that theelectrolyte solution cannot circulate freely around the electrode(limited micro-stirring effect, temperature and diffusion field aredeformed) and that a considerable portion of the heat is used forheating the substrate and so is lost. This also leads to slowed heatingand cooling of the working electrode due to the heat capacity of thesubstrate.

The disadvantage of the previous wire electrodes was, above all, thateither no microliter droplets could be deposited on them or that aconstruction with an additional plastic bar was used in which theelectrode construction (with respect to the printed circuit board) hadto be vertical. (Flechsig et al., Langmuir 21 (2005) 7848). An arrayconstruction in this way was hardly conceivable.

It was also disadvantageous that previous electrode arrays of layeredworking electrodes always consisted of identical electrode material ineach case. A design consisting of a plurality of different electrodematerials (for example, gold, silver and platinum working electrodes onan array) would have involved high production costs (sputtering,evaporation, screen printing with many changing masks).

According to the state of the art, there are also array-like deviceswith a plurality of wire-shaped working electrodes which are to beindependently heated, and which enable interference-free electrochemicalmeasurement while simultaneously electrically-heating the electrodes,whereby the electrolyte solution can circulate freely around theelectrodes. The materials of the working electrodes can vary within anarray. Similar to a conventional flat array, microliter drops can bedeposited on the electrodes and surround them (WO 2013/017635).

In order to carry out electrochemical analyses in the trace range,microelectrodes heated as in the prior art can be used. The workingelectrode must therefore be small in order to keep the mass conversionnegligibly small, thus avoiding changes in the analytical solution,which is a prerequisite in analytical voltammetry and amperometry, andalso in order to comply with the working range of thepotentiostat-galvanostat.

In order to be able to carry out electrochemical syntheses at elevatedtemperatures, electrochemical cells are generally used which are broughtto the desired temperature by means of a thermostat with water as heatexchanger. The entire quantity of electrolyte is heated in the process.A platinum electrode is generally used as the working electrode, as acylinder of 3 cm in diameter and 5 cm in length.

In electrochemical syntheses, the problem arises for the skilled workerthat firstly, a large amount of energy is needed to heat the entiresolution, secondly, the temperature changes are very slow, and thirdly,sensitive substances can be affected in the electrolyte solution. It istherefore an object of the invention to provide a device and a method toenable an electrochemical synthesis with a large conversion of materialwhich reduces or at least partially overcomes the above-mentionedproblems.

This object is achieved by the present invention, in particular by thesubject matter of the claims.

The invention provides a process for producing at least one product byelectrochemical synthesis on a directly electrically-heated workingelectrode (1), in which at least one educt reacts on the heated workingelectrode (1) to the at least one product. The invention also providesthe use of a directly electrically-heated working electrode (1) for theelectrochemical synthesis of at least one product, in which at least oneeduct reacts on the heated working electrode (1) to the at least oneproduct.

The working electrode (1) can be directly heated by means of asymmetrical arrangement with a heating current in the form of analternating current, wherein the use of a bridge circuit, as describedabove, is particularly advantageous. The symmetrical contacting anddirect heating of the working electrode (1) can therefore be effected bymeans of, for example, the bridge circuit disclosed in Wachholz et al.,2007, Electroanalysis 19, 535-540, in particular FIG. 3. In particular,the working electrode (1) can have a first and a second contact forsupplying the heating current, wherein the working electrode (1) isconnected to a potentiostat via a third contact, wherein the connectionof the third contact to the working electrode (1) is formed via a bridgecircuit (2), which is connected to the first and second contact.Suitable circuits are disclosed, for example, in DE 2006 006 347.

In order to heat the working electrode, a heating current in the form ofan alternating current can be used, in particular with a frequency of atleast 1 kHz, preferably at least 20 kHz, more preferably at least 50 kHzor at least 100 kHz.

The electrochemically active surface of the working electrode (1)preferably comprises at least 1×10⁻⁶ m², applicable for instance forsyntheses on a micro-scale, preferably 1×10⁻⁵ m² for instance on thehalf-micron scale or 1×10⁻⁴ m² for instance on the larger laboratoryscale. Electrochemically-active surfaces up to an area of one or severalsquare meters are also possible.

The fact that the volume elements of the electrolyte solution are heatedonly very briefly when they come into contact with the working electrode(1) is particularly advantageous in the process according to theinvention, the educts being converted electrochemically at the desiredelevated temperature. Even undesired subsequent reactions at hightemperature can be minimized by the rapid cooling of each volume elementdue to thermal convection. Thus, only the electrochemical reaction takesplace at elevated temperature. There is a method for chemical reactionin the gas phase in a very limited, very hot zone: see air combustion inthe electrical arc according to the Birkeland-Eyde method (1904, U.S.Pat. No. 775,123), which describes similar considerations.

A process according to the invention can be used advantageously forvarious electrochemical syntheses, for example for oxidation, reduction,substitution, dehydrogenation, addition, cleavage, cyclization,dimerization, polymerisation, protonation, deprotonation or elimination.

The at least one product of the reaction may be, for example, a proteincomprising a nitroso group, gluconic acid, sorbitol, D-arabinose,adipodinitrile, a regenerated cofactor such as NAD+ or NADP+. It isparticularly advantageous if the product of the synthesis is a productwhich is unstable at the reaction temperature at the working electrode(1), since in this case the product is exposed to this temperature onlyfor a minimal time. After synthesis on the heated working electrode, theproduct diffuses into the electrolyte, which itself is not heated to thereaction temperature. Unstable in this context means that the stabilityat the reaction temperature is lower than the stability at a lowertemperature (e.g., room temperature or 4° C.), especially for an, e.g.three- or ten-fold, lower stability relative to the difference in thereaction rate. The stability may be analyzed by, e.g. half-life. It ispossible to cool the electrolyte solution if this promotes the stabilityof the educt or product or the course of the reaction.

Within the scope of the present invention, the indefinite article “an/a”also includes “two/more”, unless it is clearly understood from thecontext to be otherwise. In particular, an electrochemical synthesis canfor example proceed via a reaction of two educts to form one or twoproduct(s) or via a reaction of one educt to form two products.

In a further advantageous embodiment, the reaction of the at least oneeduct to the at least one product can also be enzymatically catalyzed,wherein optionally the enzyme and/or a necessary cofactor is immobilizedon the heated working electrode (1). However, the educt(s), enzymeand/or cofactor can also be homogeneously distributed in the electrolytesolution. In one embodiment, a synthesis reaction takes place from atleast one product catalyzed by an enzyme that requires a cofactor suchas NAD+ or NADP+. The regeneration of the cofactor, which is necessaryfor a continuation of the reaction, takes place at the workingelectrode. In the case of enzymatic catalysis it is, of course, alsopossible to synthesize a product which is unstable at the reactiontemperature.

In an embodiment which is particularly suitable for reactions concerningthermally highly sensitive substances or in which reaction productsotherwise deposit on the working electrode, the temperature of theworking electrode can be pulse-like for up to 300 ms, e.g. about 5-250ms, 50-200 ms or 100-150 ms, but preferably less than 100 ms, above theboiling point of the electrolytes surrounding the electrode. This hasthe advantage that only a small portion of the solution is heated for ashort period of time. The thermal convection occurring briefly after theheating pulse makes stirring of the solution unnecessary. In addition,the short period of heating is beneficial for the stability of eductsand products and, if applicable, of enzymes which catalyze the reaction.In the case of unstable educts or products, this advantage plays animportant role. Furthermore, any deposits on the working electrode areremoved so that the latter cleans itself.

The process according to the invention makes it possible to monitor thematerial conversion of the reaction coulometrically. In particular,coulometric tracking of the faraday mass conversion of a synthesisreaction is possible by measuring the electrolyte current strength andcalculating the charge quantity/substance quantity as an integral of thecurrent over time.

The invention also relates to a device which comprises two insulatedconductors (3) which are connected to one another via a workingelectrode (1) which is thinner in relation to the conductors, theworking electrode (1) being formed as an anode from an electrodematerial such as a wire of noble metal, in particular gold or platinum;or a rod of carbon, for example graphite, boron-doped diamond orglass-carbon; or optically transparent conductive material, such as ITO(indium-doped tin oxide) (an electrode material), preferably gold orplatinum, wherein the working electrode (1) is preferably in the form ofa spiral, more preferably a three-dimensional spiral. In addition to thematerials mentioned, less noble metals such as copper, stainless steelor nickel can also be used as the cathode material.

The insulated conductors (3) can be, e.g. copper rods or other goodelectrical conductors, which are insulated, e.g. by a glass tube or by aplastic sheath, as is known in the art.

In a circular cylinder, a flat Archimedian spiral can be placed on theground and a screw (or helix) can be fitted into the shell as a curve.The overlap curve of the spiral and screw is referred to as a conicalspiral or cone-shaped space spiral. In an Archimedian spiral, thedistance to the center increases linearly to the increasing angle of itsorbit. If this distance is projected as an angular distance to a pole ona spherical surface, an Archimedian spherical spiral is created. It is aline of finite length, and is not identical with the loxodrome, which byits construction method resembles the logarithmic spiral (Source:Wikipedia, see also FIG. 1). A central axis can be thought of throughthe center of the spiral.

These spiral shapes can be used in the context of the invention.Advantageously, the spiral is a conical spiral, in particular a conicalArchimedeal spiral or an Archimedean spherical spiral or a loxodrome. Asection of such a spiral is sufficient, in particular in the case ofspherical spirals, it is even preferred to use only a section whichincreases or decreases (i.e. not increases and then decreases) indiameter. Irregular spiral shapes are also possible. A particularlyadvantageous embodiment is shown in FIG. 2.

In any case, a sufficient distance between sections of the workingelectrode (1) should be ensured in order to prevent short circuits. Adistance of about 1 to about 20 mm, preferably about 5 to about 15 mm orabout 8 to about 10 mm, is useful. The spacing is preferably uniformwithin the spiral. The electrical contact points between the workingelectrode (1) and the insulated conductors (3) can be locatedapproximately in the middle, i.e. on or near the central axis of thespiral. In this case, the lower and upper contact points (5, 6) arepreferably slightly laterally offset from one another. The contactpoint, which is connected to the outermost side of the spiral mostremote from the axis, can also be situated along the outer side of thespiral. If the connection of this contact point is situated within thespiral, an isolation up to the contact point on the outermost side ofthe spiral most remote from the axis can lead to an even more uniformtemperature, above all at the nearest lowest turn. Preferably, thethree-dimensional spherical working electrode is oriented with respectto the insulated conductors and, as the case may be, the furtherstructure of the device, such that the diameter of the spiral decreasesfrom the bottom to the top.

When the spiral working electrode is vertically aligned along itscentral axis in the preferred three-dimensional spiral shape, and thedevice is used for electrochemical synthesis, the working electrode ishardly, or at best is not, vertically superimposed. Therefore, throughheating of the working electrode the heated electrolyte solution doesnot meet overlying sections of the working electrode and additionallyheat them. This ensures a uniform temperature of the working electrode,which is important for the course of the synthesis.

The same effect can be achieved with a further device according to theinvention which comprises two insulated conductors (3) which areconnected to one another via a plurality of working electrodes (1) whichare thinner in relation to the insulated conductors, wherein the workingelectrodes (1) are formed as an anode of a wire of noble metal, inparticular gold or platinum; or a rod of carbon, for example graphite,boron-doped diamond or glass-carbon; or optically transparent conductivematerial such as ITO (indium-doped tin oxide) (an electrode material).In addition to the materials mentioned, less noble metals such ascopper, stainless steel or nickel can also be used as the cathode.

The working electrodes (1) are arranged so that no verticalsuperimposition of the working electrodes (1) takes place and that they

(a) are preferably essentially parallel to one another, and/or

(b) preferably extend from a lower contact point (5) with one of theinsulated conductors (3) to an upper contact point (6) offset verticallyand optionally horizontally with the other insulated conductor (3),wherein the working electrodes (1) extend outwardly from the lowercontact point (5), extend obliquely upwards in an intermediate sectionand extend inwards in an upper section towards the upper contact point(6), wherein the inclination in the middle section is arranged so thatno vertical superimposition of the working electrode sections (1) or theworking electrodes (1) occurs.

One embodiment is particularly advantageous when carbon is used as theelectrode material, e.g. glass carbon or graphite, for example in theform of a rod. In this case, the working electrode essentially has astepladder-like shape, as in the case of a rung wall, the struts ofwhich form the insulated conductors (3) and which are set obliquely inorder to prevent a vertical superposition of the working electrodes(rungs). For example, parallel glass charcoal or graphite rods, whichare arranged ladder-like, but obliquely. These parallel rods areconnected by insulated conductors, resulting in a grid-shaped workingelectrode. The rods can be fixed, e.g. by attachment to an insulatinggrid or cage. The grid or cage can be a stretched, e.g. a flat or e.g.cylindrical, shape. Also, the use of screen printing electrodes e.g. ofcarbon in parallel form, is possible.

It may be useful in an apparatus according to the invention to stabilizethe working electrodes (1) by means of an insulating carrier (7). Theinsulating carrier (7) can, for example, be a cage or a grid.Preferably, free circulation of the electrolyte by the support (7) isnot severely restricted. The insulating support preferably consists ofor comprises an insulating material, the material being glass, ceramicor plastic, e.g. Polytetrafluoroethylene (PTFE, Teflon®). If sufficientstability is ensured by the material and the shape of the electrode (1),the use of a carrier is not necessary.

The use of a two-dimensional working electrode in the method of theinvention is also possible. No vertical superposition occurs hereeither, so that a uniform temperature distribution is possible.

Preferably, the working electrode (1) has a surface area of at least1×10⁻⁶ m², preferably 1×10⁻⁵ m² or 1×10⁻⁴ m². The diameter may be e.g.about 0.05-5 mm, preferably 0.1-1 mm. The length may be about 2.5-100cm, preferably 5-50 cm, 10-40 cm, 15-30 cm or 20-25 cm. The lengthdepends on the cross-sectional area and the specific resistance of theelectrode material, so that a reasonable resistance range is maintained:the resistance between the two heating current contacts (5) and (6)should be determined, e.g. approximately 0.5 to 20 Ohm, preferably 1 to10 Ohm. In this way, the voltage drop between the contacts is on the onehand not too great, on the other hand, the resistance can still beeasily measured by means of electronics, and thus the heating power canbe automatically regulated (Flechsig, Gründner, Wang, 2004, EP 1743173,DE 10 2004 017 750 B4).

Example: the platinum working electrode has a resistance of 2 Ohm and alength of 10 cm. Then the diameter must be 82.2 microns. The electrodesurface is then 25.8 mm² as a cylinder jacket surface.

With a diameter of 1 mm, the electrode length would have to be 14.4 m,resulting in an electrode surface of 446 cm². That would be pilot plantscale.

Preferably, the working electrode (1) in the device according to theinvention is directly heated by means of a symmetrical arrangement witha heating current in the form of an alternating current. The symmetricalcontacting preferably occurs via a bridge circuit (2), as explainedabove. A symmetrically arranged inductance is provided in the connectingarms of the bridge circuit (7). By means of the bridge circuit, theworking electrode (1) can be connected with a galvanostat or apotentiostat, a reference electrode (REF) and a counterelectrode (AUX)which either functions as an anode or a cathode, depending on whether areduction or an oxidation is running on the working electrode. Thisgalvanostat or potentiostat can also be a simpler power supply devicewith a two-pole output, on the displays of which only the decompositionvoltage between the working electrode and the counterelectrode, as wellas the electrolysis current, are indicated.

Preferably, the counterelectrode (AUX) in the device according to theinvention is arranged with a distance to the working electrode of atleast 1 mm, preferably at least 5 mm, so that the thermal convectionaround and above the working electrode does not lead to a mixing of thespace around the counterelectrode, preferably it is beneath the workingelectrode. This avoids the reverse reaction of the product to the eductat the counterelectrode. In addition, unwanted products are preventedfrom coming from the counterelectrode to the working electrode. Examplesinclude in particular the halogens chlorine and bromine, but also oxygenand others. For example, it may be desirable to carry out a cathodicreduction in a chloride-containing solution at a strongly negativepotential. This would result in the oxidation of the chloride tochlorine at the counterelectrode as an anode and, depending on the pHvalue, also the formation of hypochloride. In this situation, it isadvantageous if the two electrode spaces are separated from one another,for which purpose membranes and diaphragms are used. This is alsopossible within the scope of the invention. However, the use of thelimited thermal convection according to the invention makes such aseparation by diaphragms or membranes superfluous, so that the deviceaccording to the invention preferably does not comprise diaphragms ormembranes.

For support, one can place a cooler at the bottom of the cell, e.g. acooling Peltier element.

In an embodiment of the working electrode (1) according to theinvention, the device can comprise the components shown in FIG. 2 of thepresent application. It can also comprise the components shown in DE 102006 006 347, FIG. 1, FIG. 2, FIG. 3 or FIG. 4 (preferably FIG. 1) in acorresponding arrangement.

In a particularly preferred embodiment of the method according to theinvention, the reaction proceeds on the directly heated workingelectrode of a device according to the invention, in particular a devicecomprising two insulated conductors (3) which are connected to oneanother via a working electrode (1) which is thinner in relation to theconductors, wherein the working electrode (1) is a wire of an electrodematerial such as gold, platinum and carbon (e.g. graphite, boron dopeddiamond or glass carbon) or ITO (as anode or cathode) or even less noblemetals such as copper, stainless steel or nickel (as cathode), theworking electrode (1) having the form of a spiral, preferably athree-dimensional spiral.

The invention also relates in particular to a process for the synthesisor regeneration of a cofactor of an enzymatic reaction in which thesynthesis or regeneration takes place on a directly electricallyheatable working electrode, preferably on the directly heated workingelectrode of a device according to the invention. It is also preferableto use a device which comprises two insulated conductors (3) which areconnected to one another by means of a thinner working electrode (1) inrelation to the conductors, the working electrode (1) being a wire of anelectrode material such as gold, platinum and carbon (e.g. graphite,boron-doped diamond or glass-carbon) or ITO (as anode or cathode) oreven less noble metals such as copper, stainless steel or nickel (ascathode), wherein the working electrode (1) is in the form of a spiral,preferably a three-dimensional spiral.

LEGENDS

FIG. 1 shows various forms of spirals. (A) conical Archimedean spiral(B) conical logarithmic spiral; in each case viewed obliquely from theside. (C, D) View of a working electrode (1) in the form of a conicalArchimedean spiral from above. The insulated conductors (3) are shown asthick dots. (C) shows both insulated conductors (3) in the center of thespiral, (D) shows the insulated conductors (3) with one connected to theouter side of the spiral.

FIG. 2 shows a preferred embodiment of a device according to theinvention, with a working electrode (1) shaped as a conical Achimedeanspiral. The working electrode (1) is connected to insulated conductors(3) at a lower (5) and an upper (6) contact point. The working electrode(1) is directly electrically heatable via a symmetrical arrangement,with alternating current (AC), preferably at least 50 kHz, being used asthe heating current. The symmetrical contacting is effected by means ofa bridge circuit (2). A symmetrically arranged inductance is provided inthe connection arms of the bridge circuit (7). By means of the bridgecircuit, the working electrode (1) is or can be connected with agalvanostat or a potentiostat, a reference electrode (REF) and acounterelectrode (AU/AUX), which functions either as an anode or acathode, depending on whether a reduction or an oxidation takes place atthe working electrode. This galvanostat or potentiostat can also be asimple power supply device with a two-pole output, on whose displaysmerely the decomposition voltage between the working electrode and thecounterelectrode, as well as the electrolytic current, are indicated.

EXAMPLES Example 1

According to the invention, a large area of the directly heatableworking electrode (1) for electrochemical synthesis can be achieved inthat a very long wire e.g. out of platinum or gold, or else parallelthin carbon rods, can be used as working electrodes. The workingelectrode is contacted at the ends as in the prior art, whereby aheating current of preferably at least 1000 Hz frequency, advantageouslyat least 20 kHz, more preferably 50 kHz, is used so that a bridgecircuit or a choke filter circuit known per se for separating theelectrochemical circuit from the heating circuit can be used.

(A) A Pt wire of, for example, 5 cm in length and 0.1 mm in diameter canbe spirally wound onto a cylindrical or preferably conical insulatingcage made of glass, plastic or ceramic. Such a working electrode can beused, e.g. in a reagent glass, as a cell for electrochemical synthesis.

B) A working electrode of platinum has a resistance of 2 ohm and alength of 10 cm. Its diameter is 82.2 microns. The electrode surfacearea is 25.8 mm² as the cylinder surface area.

C) With a diameter of 1 mm, the electrode length is 14.4 m, resulting inan electrode surface area of 446 cm². This already allows for synthesese.g. in a 10 to 100 L reactor, that is, in pilot-plant scale.

A wire e.g. of platinum of 1440 cm in length and 1 mm in diameter has anadvantageous heating resistance of 1 to 20, preferably 2 to 10 Ohms, andcan be used in a larger cell, e.g. in the pilot-plant scale.Advantageously, as the cage and the turns become smaller in diameter(conical rather than cylindrical), the working electrode thus has theshape of a conical spiral. This optimizes thermal convection andachieves a uniform temperature control of the working electrode. Theelectrochemical contact is located in the center, as shown in FIG. 2.

Example 2

A device according to the invention is used for

a) Selective oxidation of free amino groups to nitroso groups inproteins.

b) Oxidation of aldehyde groups in sugars to gluconic acid by anelectrochemically prepared oxidizing agent (e.g., hypobromide ofbromide), wherein e.g. heated carbon rod electrodes of graphite orglass-carbon can be used.

c) Coulometric tracking of the faraday mass conversion of a synthesisreaction by measuring the amount of electrolysis and calculating thecharge quantity/substance quantity as an integral of the current overtime.

d) For electrochemical recovery of chlorate from a solution of sodiumchloride, the solution must be heated to effect the disproportionationof the primary hypochlorite. Classically, the entire electrolytesolution is heated for this purpose. According to the invention, onlythe working electrode is heated from directly heated glass carbon rods,wherein simultaneously the solution is thermoconvectively stirred.External stirring and heating are therefore not required. Yield andenergy efficiency are improved.

Example 3

An array of electrolysis cells in combinatorial synthesis or parallelsynthesis for the screening of active substances and tests of enzymevariants.

The electrolysis cells can be structurally separated from one another orcan share a common cell space. The latter permits the simultaneous studyof immobilized enzymes in biocatalytic electrosynthesis at therespective electrode temperature; the evaluation being carried out bymeans of the measurement and evaluation of the electrolysis current.Cooling from the outside is particularly important for small cellvolumes, in order to keep the electrolyte temperature constant at thedesired value. Active cooling by Peltier elements can be helpful.Coolers from above also support thermal convection.

1. A process for producing at least one product by electrochemicalsynthesis on a directly electrically heated working electrode (1) inwhich at least one educt reacts on the heated working electrode (1) tothe at least one product.
 2. The use of a directly electrically heatedworking electrode (1) for the electrochemical synthesis of at least oneproduct, in which at least one educt reacts on the heated workingelectrode (1) to the at least one product.
 3. The process of claim 1,wherein the working electrode (1) is directly heated by means of asymmetrical arrangement with a heating current in the form of analternating current, wherein the symmetrical contacting preferablyoccurs via a bridge circuit (2).
 4. The process of claim 1, wherein theelectrochemically active surface area of the working electrode (1)comprises at least 1×10⁻⁶ m², preferably 1×10⁻⁵ m² or 1×10⁻⁴ m².
 5. Theprocess of claim 1, wherein the reaction is selected from the groupconsisting of oxidation, reduction, protonation, deprotonation,substitution, hydrogenation, dehydrogenation, condensation, hydrolysis,addition, cleavage, cyclization, dimerization, polymerization andelimination.
 6. The process of claim 1, wherein the product is selectedfrom the group consisting of a protein comprising a nitro group,gluconic acid, sorbitol, D-arabinose, adiponitrile, a regeneratedcofactor such as NAD+ or NADP+ and a product which is unstable at thereaction temperature on the working electrode (1).
 7. The process ofclaim 1, wherein the reaction of the at least one educt to the at leastone product is enzymatically catalyzed, wherein optionally the enzymeand/or a cofactor is immobilized on the heated working electrode (1). 8.The process according to claim 1, wherein a heating current in the formof an alternating current with a frequency of at least 1 kHz, preferablyat least 20 kHz, more preferably at least 50 kHz or at least 100 kHz isused for heating the working electrode (1), and/or wherein thetemperature of the working electrode (1) is increased pulse-like for upto 250 ms above the boiling point of the electrolytes surrounding theelectrode.
 9. A device comprising two insulated conductors (3) which areconnected to one another via a working electrode (1) which is thinner inrelation to the conductors, wherein the working electrode is a wire ofan electrode material selected from the group comprising gold, platinum,copper, nickel, stainless steel, lead, Hg-amalgams, indium-doped tinoxide and carbon, wherein the working electrode (1) has the form of athree-dimensional spiral.
 10. The device according to claim 9, whereinthe spiral forms a conical spiral, preferably a conical Archimedeanspiral or an Archimedean spiral coil, a loxodrome or a section of such aspiral.
 11. A device comprising two insulated conductors (3) which areconnected to one another via a plurality of working electrodes which arethinner in relation to the insulated conductors, wherein the workingelectrodes (1) are composed of an electrode material selected from thegroup comprising gold, platinum, copper, nickel, noble steel, lead,Hg-amalgams, indium doped tin oxide and carbon, wherein the workingelectrodes (1) are arranged so that no vertical superimposition takesplace and that they (a) are preferably essentially parallel to oneanother, and/or (b) preferably extend from a lower contact point (5)with one of the insulated conductors (3) to an upper contact point (6)offset vertically and optionally horizontally with the other insulatedconductor (3), wherein the working electrodes (1) extend outwardly fromthe lower contact point (5), extend obliquely upwards in an intermediatesection and extend inwards in an upper section towards the upper contactpoint (6), wherein the inclination in the middle section is arranged sothat no vertical superimposition of the working electrode sections (1)or the working electrodes (1) occurs.
 12. The device according to claim9, wherein the working electrode (1) is stabilized by an insulatingcarrier (7), wherein the insulating carrier (7) is preferably a cage ora grid, and/or wherein the insulating carrier (7) is preferably made ofan insulating material selected from the group comprising glass, ceramicor plastic, e.g. Polytetrafluoroethylene (PTFE).
 13. The deviceaccording to claim 9, wherein the working electrode has a surface areaof at least 1×10⁻⁵m², preferably 5×10⁻⁵m² or 7×10⁻⁵m², and/or a diameterof 0.1-5 mm and/or a length of 2.5-100 mm and/or a resistance of 0.5-20Ohm.
 14. The device according to claim 9, wherein the working electrode(1) is directly heated by means of a symmetrical arrangement with aheating current in the form of an alternating current, wherein thesymmetrical contacting preferably occurs via a bridge circuit (2). 15.The device according to claim 9, wherein the counterelectrode isarranged with a distance of at least 1 mm, preferably at least 5 mm,relative to the working electrode, such that the thermal convectionaround and above the working electrode does not lead to a mixing of thespace around the counterelectrode, preferably the counterelectrode islocated under the working electrode.
 16. The process of claim 1, whereinthe reaction proceeds at the directly heated working electrode of adevice comprising two insulated conductors (3) which are connected toone another via a working electrode (1) which is thinner in relation tothe conductors, wherein the working electrode is a wire of an electrodematerial selected from the group comprising gold, platinum, copper,nickel, stainless steel, lead, Hg-amalgams, indium-doped tin oxide andcarbon, wherein the working electrode (1) has the form of athree-dimensional spiral.
 17. A process for the synthesis orregeneration of a cofactor of an enzymatic reaction, wherein thesynthesis or regeneration takes place on a directly electricallyheatable working electrode, preferably on the directly heated workingelectrode of a device according to claim
 9. 18. The use of claim 2,wherein the working electrode (1) is directly heated by means of asymmetrical arrangement with a heating current in the form of analternating current, wherein the symmetrical contacting preferablyoccurs via a bridge circuit (2).
 19. The use of claim 2, wherein theelectrochemically active surface area of the working electrode (1)comprises at least 1×10⁻⁶ m², preferably 1×10⁻⁵ m² or 1×10⁻⁴ m².
 20. Theuse of claim 2, wherein the reaction is selected from the groupconsisting of oxidation, reduction, protonation, deprotonation,substitution, hydrogenation, dehydrogenation, condensation, hydrolysis,addition, cleavage, cyclization, dimerization, polymerization andelimination.
 21. The use of claim 2, wherein the product is selectedfrom the group consisting of a protein comprising a nitro group,gluconic acid, sorbitol, D-arabinose, adiponitrile, a regeneratedcofactor such as NAD+ or NADP+ and a product which is unstable at thereaction temperature on the working electrode (1).
 22. The use of claim2, wherein the reaction of the at least one educt to the at least oneproduct is enzymatically catalyzed, wherein optionally the enzyme and/ora cofactor is immobilized on the heated working electrode (1).
 23. Theuse according to claim 2, wherein a heating current in the form of analternating current with a frequency of at least 1 kHz, preferably atleast 20 kHz, more preferably at least 50 kHz or at least 100 kHz isused for heating the working electrode (1), and/or wherein thetemperature of the working electrode (1) is increased pulse-like for upto 250 ms above the boiling point of the electrolytes surrounding theelectrode.
 24. The use of claim 2, wherein the reaction proceeds at thedirectly heated working electrode of a device comprising two insulatedconductors (3) which are connected to one another via a workingelectrode (1) which is thinner in relation to the conductors, whereinthe working electrode is a wire of an electrode material selected fromthe group comprising gold, platinum, copper, nickel, stainless steel,lead, Hg-amalgams, indium-doped tin oxide and carbon, wherein theworking electrode (1) has the form of a three-dimensional spiral.